On Wed, Sep 16, 2009 at 07:44:07AM +1000, Benjamin Herrenschmidt wrote:

On Tue, 2009-09-15 at 11:32 -0400, Josh Boyer wrote:

quoted

On Tue, Sep 15, 2009 at 10:31:36AM -0400, Paul Gortmaker wrote:

quoted

One of the guys here was getting a messed up console on a bamboo board
(on linux boot), which he traced to the fact that the default dts has a
9600 baudrate coded into it (board was running 115k2, not 9600).  Either
deleting the line, or replacing the 9600 with zero fixed the problem.

Once booted, was there a valid current-speed property in /proc/device-tree
for the serial node?  I'm curious if U-Boot created it, or if the kernel
just used whatever baud was present already.

When I did the bamboo port a while ago, I recall having issues with either
a missing clock-frequency or current-speed (or both perhaps) and the bootloader
on the board was the original PIBS.  It might have been an issue with PIBS
but I'm guessing the rest of the 4xx boards copied from either Ebony or
Bamboo in their ports and hence contain that property.

I think I recently added code to legacy_serial probe the speed from the
HW if the property is absent, which should help.

Ok, so I think that is related to what I originally hit.

I played around with removing the current-speed property on canyonlands today,
and noticed that I would get no console output at all unless I specified a
baudrate with console=ttyS0,115200.  That was sort of contrary to what I found
with bamboo, so I diffed the configs to see why.  Bamboo has udbg enabled and
hence has legacy_serial builtin, whereas canyonlands just has of_serial.

So on boards where of_serial is the only serial driver, we need either an
accurate current-speed property, or a specific baudrate on the command line.
That makes a bit more tenuous to remove the properties entirely, because if
people disable udbg and are relying on that behavior they get no more console
output.  Need to think on that a bit I guess.

Alternatively, we could try patching of_serial.c to do the baudrate probe
as well.

josh